CIBJO releases Gemmological Special Report: considers process of separating measurable facts from opinion; See Gemological Articles below.
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 Post subject: Gemstone Processing
PostPosted: Wed Jan 30, 2013 11:30 am 
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I'm contacting you today in an effort to appeal to your expertise in gemstone furnace processing. I work in a laboratory quality processing synthetic gemstones, using a Lindberg-Blue M 1700 Degree tube furnace, model number STF54434C. While processing specific gemstones, I'm repeatedly encountering small, brown stains, resembling that of a coffee stain on printing paper, spread accross the surface of the stone.

Through experimentation we've eliminated the cleaning process as a factor contributing to the stains, but for good measure, our cleaning process is a 6 minute soak in Citrinox, followed by a six minute clean rinse and ample drying with oxygen pumping through a gentle spray nozzle. The stones are then placed into a tube furnace that gradually heats up to 1300 degrees Fahrenheit, hovers at that temperature for 6 minutes, and gradually drops back down, a process that we have determined to be ideal, along with an accurate calibration of the furnace itself. (A cooking process which takes roughly 50 minutes) Previously we were using Nitrogen to fill the furnace atmosphere which proved to aid in the ending quality of the stones. Nitrogen proved to be instrumental in achieving a higher quality and was working quite well, until we eventually were made aware of the aforementioned brown surface blemishes.

With the use of an average 10x loop, and when the stone is angled correctly, a very small light brown stain can be seen on many of the stones that emerge out of a batch from the furnace. Larger clients have begun returning stones because of these small stains, and it seems as though we have eliminated all potential catalysts as to what is causing these stains. The reason I am addressing you today was due to the fact that we ordered Argon to fill the furnace atmosphere as an alternative in hopes of resolving the issue, to no avail. In your experience, have you ever come across such an issue with a final product after treatment in a furnace? If so, might you be able to offer any insight into what is causing the issue?

Alternatively, these brown spots are able to be removed with a resource-exhaustive and time intensive process; using a simple soak and scrub in an industrial sonic and acetone has proven minimally effective. Might you have any knowledge of a cleaning agent that may be more effective and efficient?

Thank you for your time.


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 Post subject: Re: Gemstone Processing
PostPosted: Wed Jan 30, 2013 2:28 pm 
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Try DMSO.


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 Post subject: Re: Gemstone Processing
PostPosted: Wed Jan 30, 2013 3:47 pm 
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Bill Hanneman wrote:
Try DMSO.

DMSO?

My apologies, I'm new to the industry.


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 Post subject: Re: Gemstone Processing
PostPosted: Wed Jan 30, 2013 11:07 pm 
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Dimethylsulfoxide. I haven't used it for 30 years, so it would not surprise me if no one will let you use it today.


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 Post subject: Re: Gemstone Processing
PostPosted: Thu Jan 31, 2013 12:53 am 
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DMSO is still standard for some organic chemistry and other applications. It's not too dangerous or restricted to put in the hands of low-level undergraduate orgo students, but it's not particularly nice stuff either.

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 Post subject: Re: Gemstone Processing
PostPosted: Thu Jan 31, 2013 1:17 am 
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When I was doing a lot of jewelry repair I'd eventually be unable to get a clients jewelry clean enough and, thinking it was clean, I'd heat it up with a torch to do some work. Oily residue would invariably spread over parts of the piece, leaving a stain as you describe. I would generally be successful in removing all but the most burned on char by soaking the piece in oven cleaner, (aka lye). I would place the piece in a large test tube, spray the oven cleaner to cover the piece and let it sit in the ultrasonic cleaner for a while.

If the material is too charred for this to work, you could always add some oxygen to your furnace and burn the junk off, (just pretend it's a burn out furnace, since 1300 is about the same temp used to burn out wax residue from casting molds).

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 Post subject: Re: Gemstone Processing
PostPosted: Thu Jan 31, 2013 9:31 pm 
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Bill Hanneman wrote:
Dimethylsulfoxide. I haven't used it for 30 years, so it would not surprise me if no one will let you use it today.

Bill, despite all the efforts to protect the public from anything useful, DMSO is actually sold on Amazon:
http://www.amazon.com/DMSO-Pure-99-Liquid-16/dp/B000O5FRF4/ref=pd_sim_sg_6

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